The control of diesel engine emissions through aftertreatment systems typically involves the use of technology such as a diesel particulate filter for control of particulates and a lean-NOx trap (LNT) or selective catalytic reduction (SCR) for NOx control. Hydrocarbon (HC) based reagents like diesel fuel can be injected into a diesel engine exhaust to assist in regenerating and burning off soot collected in a Diesel Particulate Filter (DPF) or to provide fuel rich conditions across a LNT for the chemical reduction of NOx stored as NO2. Reagents such as urea or ammonia solutions in water are generally used to chemically convert NOx across a vanadium, precious metal or zeolite catalyst to harmless nitrogen gas. These systems all rely on the precise control and injection of reagents into the exhaust across a broad range of reagent flow rates tied to engine operating and aftertreatment operating conditions. Further, the varying engine sizes from less than 2 liters in passenger cars up to 16 liters in heavy duty trucks each requires different amounts of metered reagent to be injected into the exhaust leading to a wide array of differing injector sizes and designs for each different application, thereby increasing production, inventory and service costs.
It would be advantageous to provide a simple system with a controller able to take engine signals such as rpm, load, exhaust temperature or backpressure from an engine ECU and to control one or more pumps feeding one or more injectors injecting HC or urea separately or concurrently at one or more locations in the exhaust pipe of a diesel engine.
Some systems are known that include a controller for injecting a reagent based on parameters such as temperature and pressure. For example, U.S. Pat. No. 6,361,754 to Peter-Hoblyn et al. (“the Peter-Hoblyn patent”) discloses a system for reducing emissions that includes a controller for modulating the flow or pulse of reagent injection ports or nozzles. However, the system disclosed in the Peter-Hoblyn patent does not provide for the injection of two different reagents and, in fact, only injects gaseous ammonia formed from the hydrolysis of aqueous urea in an upstream process.
U.S. Pat. No. 7,264,785 to Blakeman et al. (“the Blakeman patent”) describes a system for selective catalyst reduction including means for injecting a nitrogenous reducing agent, ammonia, at multiple locations in an exhaust stream. The Blakeman patent further discloses a means for controlling the introduction of the ammonia. However, the disclosed system only injects one reducing agent into the exhaust stream, and only in one location at any given time. In particular, the system injects ammonia in a first area of exhaust stream then switches to a second area when a particular temperature is reached. The system described in the Blakeman patent also uses gaseous ammonia and requires a complex catalytic conversion of urea to gaseous ammonia across a hydrolysis catalyst. The Blakeman patent further describes a complex means of injecting urea when the engine is keyed off and storing urea in a catalyst until the engine is keyed on.
International Patent Application Publication WO 2004/058642 to Valentine (“the Valentine application”) discloses a NOx control system for internal combustion engines. The system includes two or more catalysts and injectors for injecting a reagent in two different zones upstream of the catalysts. A controller takes measured parameters and compares them to reference values to create control signals that can optimize reagent utilization. In particular, the controller switches the location of reagent from the first zone to the second as necessary based on gas temperatures. As in the other cited prior art, only a single reagent is employed. Furthermore, the Valentine application does not disclose how the wide range of reagents needed for engine operating conditions could be met given the single injector in front of each catalyst. The temperature limitations of each catalyst would prevent simultaneous injection using both injectors for high flow rates.
It would also be advantageous to provide an injector having the capability of a wide range of flow rates from 0.25 to 600 grams/min. It would be further advantageous to be able to provide two injectors which in combination are capable of delivering up to 1200 grams/min. It would be still further advantageous to be able to change the flow range by physically changing only a removable orifice plate with a range of orifice sizes (0.004-0.030″) and by varying operating parameters of percentage on-time (1%-95%), or operating frequency (1-10 Hz) or operating pressure (60-120 psi). In addition, it would be advantageous if such an injector did not require air for atomization or cooling and was constructed of materials capable of injecting either HC or urea based reagents into exhaust gas having temperatures of 150 C. to 800 C. with a minimum of dwell spaces to prevent deposits from forming or collecting in the injector. It would further be advantageous if injection of reagents could be done without complex catalytic pre-treatment of reagents.
The methods and apparatus of the present invention provide the foregoing and other advantages.